FIG. 12 shows a double-effect absorption chiller which comprises an upper shell 1 comprising a condenser 11 and low temperature generator 12, a lower shell 2 comprising an evaporator 21 and absorber 22, a high temperature generator 3 incorporating a burner 31, a high temperature heat exchanger 4, a low temperature heat exchanger 5, etc. These components are interconnected by piping to recycle an absorbent through the high temperature generator 3, low temperature generator 12 and absorber 22 by an absorbent pump 6 and realize refrigeration cycles.
With the chiller of the type described, a pipe 7 for supplying the refrigerant liquefied by the low temperature generator 12 to the condenser 11 therethrough is provided with an orifice 70 as shown in FIG. 13 to reduce the pressure of the refrigerant liquefied by the generator 12 before the refrigerant is supplied to the condenser 11. Thus, the generator 12 is maintained at a low internal pressure so that the vapor of refrigerant produced in the generator 12 is liquefied on condensation in the condenser 11.
On the other hand, the high temperature generator 3 produces vapor of refrigerant, which is condensed in a heat transfer tube within the low temperature generator 12 to liquefy while giving the heat of condensation to the absorber. The liquefied refrigerant is supplied to the condenser 11 via the orifice 70 and then returned to the evaporator 21 along with the portion of refrigerant which is liquefied in the condenser 11.
As shown in FIG. 12, a gas valve 32 is mounted on a pipe for supplying a fuel gas to the burner 31 of the high temperature generator 3. The opening degree of the gas valve 32 is controlled to adjust the rate of supply of the fuel gas in order to maintain the temperature cold water outlet temperature Tc_out) of cold water flowing out of the evaporator 21 at a target value.
With the double-effect absorption chiller, it is ideal that the heat input to the high temperature generator 3 cause the generator 3 to produce an amount of vapor corresponding to the quantity of heat input for the amount of vapor to produce vapor having the same quantity of heat in the low temperature generator 12. A maximum efficiency is achieved at this time. To obtain a state as close as to the ideal, it is necessary to optimize the diameter of the orifice 70 to effect a suitable pressure reduction. The optimum pressure reduction varies with the magnitude of the refrigeration load.
Since there is an approximate proportional relationship between the amount of vapor released from the absorbent and the absorbent concentration difference between the inlet and the outlet of the low temperature generator 12 and the high temperature generator 3, an efficiency approximate to a maximum is obtained when the concentration difference between the absorbent (strong solution) in the low temperature generator 12 and the absorbent (intermediate solution) in the high temperature generator 3 is equal to the concentration difference between the absorbent (weak solution) in the absorber 22 and the absorbent (intermediate solution) in the high temperature generator 3.
However, since the conventional double-effect absorption chiller uses a fixed orifice of definite diameter as the orifice 70, the pressure reduction differs from the optimum value with variations in the refrigeration load.
Further when the absorption chiller is started up, the flow rate of refrigerant from the low temperature generator 12 becomes greater than in the state of stabilized load, so that the orifice 70 used has a greater diameter than is optimum in view of the increase in the flow rate. The conventional chiller of the type described therefore has the problem that while the chiller is in operation with a stabilized refrigeration load after the start-up, the pressure reduction becomes insufficient to result in a lower efficiency. The chiller has another problem that when the refrigeration load decreases, impairment of the efficiency becomes pronounced owing to the escape of vapor.
When remaining unchanged in con cent ration, the absorbent evaporates more easily at a lower temperature because of a drop in boiling point. Accordingly, it is possible to adjust the amount of evaporation by controlling the pressure. However, the pipe 7 for supplying the refrigerant liquefied in the low temperature generator 12 to the condenser 11 is merely provided with the orifice 70 of definite diameter, so that the conventional double-effect absorption chiller is not adapted for the active control of pressure. As a result, even if the high temperature generator 3 and the low temperature generator 12 are rated at a ratio of 1:1 in the amount of evaporation when designed, this balance of 1:1 is upset due to variations in the refrigeration load, leading to a lower efficiency.
Further with the chiller of the type described, the absorbent (intermediate solution) in the high temperature generator 3 is supplied to the low temperature generator 12 by virtue of the pressure difference between these generators 3 and 12, whereby the concentration of the absorbent (strong solution) collected in the low temperature generator 12 is determined. Thus, the concentration of the strong solution is not controlled positively. Nevertheless, the lower the concentration of the strong solution, the greater the flow rate of the recycling absorbent is, entailing an increased energy consumption for the rise of sensible heat of the absorbent, hence the problem of impaired efficiency.
An object of the present invention is to provide a double-effect absorption chiller which achieves a higher efficiency than conventionally regardless of the operating conditions such as refrigeration load.
Another object of the invention is to provide an absorption chiller which is adapted to pass the refrigerant to the condenser without stagnation when the chiller is started up or in the event of a sudden increase in the load and which is capable of giving a suitable reduced pressure to the refrigerant during steady-state operation so as to achieve a higher operating efficiency than in the prior art.
Another object of the invention is to positively control the concentration of the strong solution to achieve an improvement in operation efficiency over the prior art.